The present invention relates to a mold for molding and vulcanizing of a rubber tire.
In the manufacture of new tires, one type of mold has become of general use: It comprises two side parts, each serving for the exterior molding of a sidewall of a tire and, for the exterior molding of the tread, a peripheral ring divided into a plurality of segments having side faces perpendicular to the axis of the mold and radial transverse faces (see, for instance, U.S. Pat. No. 3,779,677). In order to close such a mold, the segments must be displaced radially towards the axis and the side parts brought axially towards each other. In the closed position these various members (side parts and segments) adjoin each other and define the exterior surface of the tire. The raw rubber blank of the future tire must be firmly applied and held against the mold in order to obtain the desired geometrical dimensions and in order, where applicable, to impress the pattern of the tread. For this, there is customarily used a flexible rubber membrane which is applied against the interior surface of the raw rubber blank by inflation to the required pressure, and which causes or tends to cause an expansion of the blank. In order to assure a molding of good quality, it is necessary that the raw rubber blank be subjected to a molding pressure of about 10 bars. This pressure is applied via the membrane. In order to limit the molding burrs as much as possible, it is desirable that the increase in pressure of the membrane take place only when the mold is in closed position. In order to avoid the appearance of these burrs, Canadian Patent No. 765,745 proposes making segments having parallel transverse faces. The peripheral ring therefore has alternately segments with parallel transverse faces and segments whose transverse faces are parallel to the transverse faces of the adjacent segments. Thus, at the end of the closing of the mold, the segments with parallel transverse faces can slide between the other segments, in the manner of a piston, which makes it possible to avoid pinching the raw rubber blank between two adjacent segments.
The molding and the vulcanizing of a rubber tire with the classical means, namely a segment mold for defining the exterior surface of the tire and a flexible rubber membrane to define the interior surface of the tire does not make it possible fully to control the shape and interior dimensions of the tire.
Another drawback resulting from the use of the molding and vulcanizing techniques of the prior art relates to the different thermal behaviors of the different members in contact with the tire during the vulcanizing, i.e., the metallic side parts and the peripheral ring of metal segments, on the one hand, and the rubber membrane, on the other hand. This complicates the establishing of the laws of vulcanization as well as the placing of them into practice.
On the other hand, it is also known to use a removable rigid core to define the interior surface of the blank of the future tire. By way of illustration, reference will be had, for instance, to U.S. Pat. No. 1,877,751. The rigid cores at times define a non-deformable molding space together with the exterior member. In practice, they can be used for the production of tires only by pouring or injecting a material in liquid or pasty state into the molding space. This is the process for the production of polyurethane tires which is illustrated, for instance, by U.S. Pat. No. 4,279 856.
However, if the rigid core supports a non-vulcanized tire blank made with the materials conventionally used in the tire industry (namely non-vulcanized rubber, textile and/or metal reinforcement elements), and this rigid core is associated with a segment mold of the customary type described in U.S. Pat. No. 3,779,677, the segments start to penetrate into the raw blank so as to impress the tread pattern therein well before the complete closing of the mold. When the mold is not completely closed, spaces are present between all the segments. The raw rubber can thus flow between the segments. Depending on the grooving ratio of the tread pattern and the resultant movements of raw rubber, this flow will cause extensive burrs and even the impossibility of assuring the proper closing of the mold due to the excessive amount of rubber present in the spaces, preventing the relative circumferential bringing together of the segments which is necessary in order to permit their radial movement up to complete closing.